Design and experiment of the seed-liquid tank of pneumatic agitation fluid seeder

Drought has seriously threatened the normal sowing and seed germination of dryland crops, such as corn and cotton. The fluid seeding can suspend the seeds in a mixture, named as seed-liquid of water and high absorbent polymer (HSP), which can absorb water when high in moisture and slowly release water when lacking. A favorable condition can then provide for the germination and emergence of the crop. The seed damage rate can be reduced for high yield, due to the drought resistance, water conservation, and high emergence rate. It is often required for the uniform distribution of the seeds in the liquid for the fluid seeding quality. Pneumatic agitation can be utilized to generate the flow field for the suspension of the seed. However, the flow field can be confined to the structure of the seed-liquid tank. In this study, four seed-liquid tanks were designed to develop the pneumatic-agitation fluid seeder, including the shapes-square (SQ), triangular type (TRA), quasi wedge (QW), and quasi wedge-arc (QWA). The air was then supplied through the air inlet at the bottom of the seed-liquid tank during operation. A model was also established to determine the relationship between the air consumption for the pneumatic agitation and the structural parameters of the tank. CFD simulation was finally carried out to explore the effect of the vertical section shape of the seed-liquid tank on the flow field of the seed-liquid under various air inlet speeds. The results show that the SQ seed-liquid tank shared the dead space in the circulation, leading to the seed deposition; In the TRA seed-liquid tank, an overall circulation failed to the uniform distribution of seeds, leading to the unstable seed-liquid flow field in the middle and lower parts of the tank; The QW seed-liquid tank shared the multiple small vortices on the flow field of the seed liquid; And the QWA seed-liquid tank exhibited an optimal performance at all air inlet speeds, in terms of the seed-liquid circulation patterns, flow field stability, and the less circulation dead space; Once the inlet air speed was constant, the maximum and minimum ratio of the seed-liquid flow speed varied in a range of 0.04, indicating the minimal fluctuations and optimal stability in the flow speed. An experiment was conducted on the QWA seed-liquid tank to verify the simulation. The stability of the seed-liquid flow field was optimal at the inlet air speed of 4 m/s. There was a relative error of 9.30% between the simulated and the tested flow speed at the ideal area of the seed outlet in the seed-liquid tank. The gas-liquid flow model was simplified to verify the reliability. The pneumatic agitation test was conducted at varying rates of air flow. The theoretical calculations were verified to observe the distribution of the seeds in the seed-liquid tank. The seed deposition decreased at an inlet air flow rate of 1.5 and 2.0 m³/h, and then the seed was distributed relatively uniformly in the liquid, and the corresponding air consumption was 6.67×10^-3 and 8.89×10^-3 m³/h, which was consistent with the predicted value. The finding can provide a strong reference for designing the seed-liquid tanks during fluid seeding.